Obligate parasite

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This topic is discussed in the following articles:

bacteria

Some bacteria are obligate parasites and grow only within a living host cell. Rickettsia and Chlamydia, for example, grow in eukaryotic cells, and Bdellovibrio grow in bacterial cells. Treponema pallidum is difficult, if not impossible, to grow in culture, probably because it...

communicable diseases

Most pathogenic bacteria are obligate parasites; that is, they are found only in association with their hosts. Some, such as staphylococci and streptococci, can proliferate outside the body of the host in nutritive materials infected from host sources. Within the tissues of the host, these organisms set up local infections that spread throughout the body. Still other bacteria, such as the...

fungi

...the intercellular hyphae and penetrate the cells themselves. Haustoria, which may be short, bulbous protrusions or large branched systems filling the whole cell, are characteristically produced by obligate (i.e., invariably parasitic) parasites; some facultative (i.e., occasionally parasitic) parasites also produce them. Obligate parasites, which require living cytoplasm and have extremely...

viruses

...several shapes, and are widely distributed in nature, infecting animal cells, plant cells, and microorganisms. The field of study in which they are investigated is called virology. All viruses are obligate parasites; that is, they lack metabolic machinery of their own to generate energy or to synthesize proteins, so they depend on host cells to carry out these vital functions. Once inside a...

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